1. Field of the Invention
The present invention relates to a fuel injector for an internal combustion engine. More particularly, the invention relates to a fuel injector for an internal combustion engine provided with a pressure control valve for controlling fuel pressure to be reduced in a fuel rail, the fuel of the internal combustion engine being pressured and accumulated in the fuel rail.
2. Description of the Related Art
To increase fuel pressure in a fuel rail during the normal operation of an engine, pressure feeding of fuel by use of a high pressure fuel pump is known. On the other hand, to decrease fuel pressure in the fuel rail, the pressure feeding of fuel by use of the high pressure pump is stopped, and the fuel is injected into each cylinder from a fuel injection valve to decrease the fuel pressure in the fuel rail. This method is generally used in the field. Such a method is intended to inject fuel only for the purpose of decreasing fuel pressure. As a result, fuel is uselessly consumed.
In contrast, JP-A-7-158536 discloses a technique in which a fuel relief valve adapted to discharge fuel when an engine is stopped is disposed in a fuel rail for use in a fuel injector for injecting fuel into each cylinder from the fuel rail through a fuel injection valve, the fuel rail accumulating the pressured fuel pressure fed by a high pressure fuel pump.
Such a fuel supply unit controls the fuel pressure such that when the fuel pressure in the fuel rail becomes higher than a specified value, a pressure control valve is opened to discharge fuel from the fuel rail until the fuel pressure becomes lower than the specified value.
However, the technique disclosed in JP-A-7-158536 can be used only when the engine is stopped.
Alternatively, JP-A-10-54318 discloses a fuel supply system in which a fuel relief valve is disposed in a fuel rail, and the fuel pressure is controlled such that when the fuel pressure rapidly decreases, one pulse is supplied to the relief valve, whereas when the fuel pressure gently decreases, an on/off pulse whose on duty is constant is supplied to the relief valve.